Beta cell transplantation potentially provides the ultimate cure for type I diabetes. However, the limited availability of donor beta cells constrains the use of this treatment as a clinical therapy. Pluripotent stem cells can proliferate infinitely and differentiate into many cell types; thus, PS cells are a promising source for beta cells. However, before PS cells can be used to treat diabetes, they need to be efficiently and reproducibly differentiated to pancreatic cells.
During vertebrate embryonic development, a pluripotent cell gives rise to the three germ layers; ectoderm, mesoderm and endoderm. Induction of definitive endoderm (DE) is the first step towards formation of endoderm derived tissues. Generation of pancreatic endoderm (PE) from DE cells is necessary for the generation of insulin-producing beta cells. PE cells with the potential to become endocrine progenitors (EP) are characterized by co-expression of two important transcription factors, PDX1 and NKX6.1.
Stepwise in vitro differentiation protocols have been established for generating pancreatic cells from PS cells. These protocols generally mimic the major events of pancreatic development, which includes several stages such as formation of the DE which co-expresses SOX17 and FOXA2, primitive gut, posterior foregut, PE, EP and ultimately the mature beta cells. To date, efficient DE differentiation of hES cells has been achieved by activin A treatment. The next major step in generating pancreatic beta cells is to generate PE that co-expresses PDX1 and NKX6.1. Several groups have developed in vitro protocols that can differentiate PS cells into DE and PE, however they are only able to generate a modest fraction of NKX6.1/PDX1 double positive (db+ve) cells, and importantly none of them are able to generate fully mature beta cells in vitro (Cai et al. (2010); D'Amour et al. (2006); Kunisada et al. (2012); Schulz et al. (2012); Zhang et al. (2009); Ameri et al. (2010)).